Tewameter® TM 300

• The Measuring Principle

  A certain evaporation of water from the skin takes always place as part of the normal skin metabolism. As soon as the barrier function of the skin however is slightly damages, the waterloss will increase (even with smallest damages invisible to the human eye). Therefore this measurement is a basis for all cosmetic and dermatological research. The Tewameter® probe measures the density gradient of the water evaporation from the skin indirectly by the two pairs of sensors (temperature and relative humidity) inside the hollow cylinder. This is an open chamber measurement. The open chamber measurement method is the only method to assess the TEWL continuously without influencing its micro environment. A microprocessor analyses the values and expresses the evaporation rate in g/h/m2.

   

   

   

   

   

   

  A = surface [m2]

   

  m = water transported [g]

   

  t = time [h]

   

  D = diffusion constant [= 0.0877 g/m(h(mmHg))]

   

  p = vapour pressure of the atmosphere [mm Hg]

   

  x = distance from skin surface to point of measurement [m]

  

• Advantages of the Tewameter®

  • Extremely accurate and quick measurement of the TEWL without any influences of the micro climate of the skin (pressure, occlusion, temperature)

  • The small size of the probe head minimizes the influence of air turbulence inside the probe.

  • Its low weight has no influence on the skin structure and ensures easy handling.

  • No waiting time between the measurements

  • Traceable, sophisticated calibration of humidity, temperature and TEWL to g/h/m2

  • A stable measurement is achieved quickly; continuous measurements over longer periods are also possible depending on the application.

  • The development of the measurement values and average and standard deviation over time are always visible. Display of r.h and °C separately for upper and lower sensor

  • Worldwide most used TEWL measurement method (even approved in space!!). Several hundreds of performed studies with the Tewameter® proof this fact.

  • Recording of the ambient conditions with the Ambient Condition Sensor RHT 100 to help to compare measurements taken at different times

  • Special calculations i.e. SSWL (Skin Surface Water Loss - assessment of skin's water holding capacity after occlusion) are possible

  • With the open chamber measurement even  higher waterloss values can be detected accurately as no water is collected inside the probe.

  • Accuracy of the probe can be checked anytime quickly

  • Offset function to compensate "aging effects" of the probe

  • Measurement with several probes at the same time possible (e.g. for the measurement of large areas or sweat studies)

  • Accessories for measurements on small skin areas, wounds etc. are available

  • The worldwide only TEWL measurement device to measure with open and closed chamber (by a special adapter cap)

  

  

  

• Fields of Application

  The measurement of the TEWL and the quality of the barrier function of the skin is the basic measurement for all  cosmetic applications.

   

  • Indispensable instrument for formulation, claim support and efficacy testing of skin care, household product, raw materials and pharmaceutical products

  • Scalp, lip and hair measurements

  • Sweat studies (Anti-Transpirant efficacy)

  • It can be used in in vitro testing of skin permeability and dermal absorption necessary for safety and efficacy testing. For this application even a special probe, the In-vitro Tewameter® VT 310 has been developed.

  • It is used for dermatological basic research.

  • In occupational health it is used to show the quality of the barrier function of the skin and the importance of using skin protection products.

  • Veterinary dermatology and zoology.

  • The measurement is also used in related industries such as textile or food or paper/tissue industry

  

  

  

• The Probe Heater PR 100

  The sensors of the probe normally have room temperature (20-22°C), whereas skin temperature is 30°C and higher. As the amount of evaporating water measured with the device is extremely small (healthy skin 8-15 g/h/m² → 0.000001333 - 0.00000025 g/minute/cm²), the sensors inside the probe should reach skin temperature to measure this small amount exactly and stable. With the probe heater the probe head is constantly warmed up to a temperature close to skin temperature and thus getting very quickly accurate and stable results. The probe heater can of course also be used for other C+K probes.

  

  

  

• In-vitro Measurements with the Tewameter®

  With the In-vitro Tewameter® VT 310 a probe for the TEWL measurement is available, which offers all benefits of the Tewameter® and is perfectly suited to sit on a Franz cell. It emulates completely the upper part (donor chamber) of a Franz cell (standard is 15 mm Ø, other sizes on request).Thus the probes sits exactly on the membrane of the Franz cell as it would sit on skin directly without needing further adapters.

   

  The measured TEWL-value is expressed in g/h/m², the worldwide acknowledged absolute measuring value for skin.

  No other probe offers this possibility.

   

  If needed, the probe can also be used on a centerpiece of high quality Teflon, which fits exactly on the probe and the receptor chamber of the Franz cell without further fixing adapters. The thus measured TEWL has to be regarded relatively (no longer absolute figures as the distance between probe and membrane is changed).

  

  

  

  

  In-vitro TEWL measurements have a variety of different applications:

   

  • inexpensive pre-screening before in vivo tests (no ethic commission, no expensive volunteers)

  • only way to study skin permeability and dermal absorption necessary for safety and efficacy testing

  • in vitro tests are established in several worldwide acknowledged guidelines: WHO (World Health Organization), SCCS (Scientific Committee on Consumer Safety) and OECD (Organization for Economic Cooperation and Development.

• Closed Chamber Measurements with the Tewameter® TM 300

  The Tewameter® is the worldwide only device which measures with open chamber as well with closed chamber by a special semipermeable adapter cap. The closed chamber is useful for measurements under suboptimal environmental conditions like in field tests or in some occupational surroundings to minimize air turbulences inside the probe.

  

• Special Accessories for the Tewameter® TM 300

  There are specials adapters available for the probe.

   

  One adapter with smaller opening is available for different applications e.g. measurement on small animals or small skin sites (reduced the measurement area to 2 mm Ø).

   

  Special steel rings are available when measuring on wounds or special surfaces. They can be mounted on the measuring head and after the measurement taken off the probe and be disinfected.

  

  

  The Tewameter® TM 300 is available as a stand-alone device or connectable to the MPA systems or as a wireless probe.

   

  Other related probes available:

  TEWL measurement probe  with three measurement chambers, the Tewameter® Triple TM 330T.

  In-vitro Tewameter® VT 310 to measure directly on Franz cells

  

  

• Technical Data

  Probe only:

   

  Dimensions: Measuring Chamber: 2 cm, Ø 1 cm, Probe: 15.3 cm, Cable length: approx. 1.3 m, Weight: 90 g, Resolution: Humidity: ± 0.01 % RH, Temp.: ± 0.01 °C, TEWL: 0.1 g/h/m²

   

  Accuracy for TEWL-values lower than 70 g/h/m²:

   

  rel. humidity (r.h.): ± 1.5 % for r.h. between 30 % and 90 %, ± 2.5 % for r.h. between 90 % and 100 % and for r. h. between 10 % and 30 %

   

  Waterloss: ± 0.5 g/h/m² for r.h. ≥ 30 %; ± 1.0 g/hm² for r.h. ≤ 30%,

   

  Temperature: ± 0.5 °C

   

  Probe Heater PR 100: Power supply: external 100-240 VAC, 47-63 Hz, DC 12V/4A,  Dimensions: 10 x 11 x 10.5 cm Weight: 470 g

   

  Operating conditions: T: 10-40° C r.H.: 30-70 % RH,

   

  For the dimensions, etc. of the wireless probes, please see the technical data of the basic devices.

   

  Technical changes may be made without prior notice.